Image sensors comprising arrays of photosensitive elements separated by a non-photosensitive intervening region

ABSTRACT

Among other things, an integral image sensor includes a sensor surface having a surface area at which light-sensitive pixels are arranged in rows and columns. The surface area includes two or more light-sensitive subareas each of the subareas having been configured to have been diced from a wafer along two orthogonal dimensions to form a discrete image sensor. The two or more light-sensitive subareas are arranged along one of the two orthogonal dimensions. The sensor surface of the integral image sensor is flat and continuous across the two or more subareas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application and claims priority toU.S. application Ser. No. 16/837,640, filed on Apr. 1, 2020, which is acontinuation application and claims priority to U.S. application Ser.No. 16/514,346, filed on Jul. 17, 2019 (now U.S. Pat. No. 10,644,054,issued on May 5, 2020), which is a continuation application and claimspriority to U.S. application Ser. No. 16/282,501, filed on Feb. 22, 2019(now U.S. Pat. No. 10,461,112, issued on Oct. 29, 2019), which is acontinuation application and claims priority to U.S. application Ser.No. 16/210,098, filed on Dec. 5, 2018 (now U.S. Pat. No. 10,249,669,issued on Apr. 2, 2019), which is a divisional application of and claimspriority to U.S. application Ser. No. 15/963,894, filed on Apr. 26, 2018(now U.S. Pat. No. 10,153,317, issued on Dec. 11, 2018).

BACKGROUND

This description relates to image sensors.

Individual discrete image sensors used in digital camera applications,for example, are typically obtained from a wafer on which the sensors,formed in rows and columns, are separated by dicing the wafer. In somedicing processes, slices are made in two orthogonal directions acrossthe wafer to form saw streets between the rows and columns of sensors.Each image sensor has an array of light-sensitive pixels usuallyarranged in rows and columns parallel to the rows and columns alongwhich the sensors themselves are arranged. When the sensors are formedon the wafer, subareas that do not contain light-sensitive pixels areformed between the sensors to provide space for the dicing slice or kerfto be made without damaging the sensors. To incorporate a sensor into acircuit electrical connections are made from the circuit tointerconnection contacts that are typically arranged along two or moresides of the sensor.

Image sensors are sometimes used in applications that do not includelenses between the object and the sensor, for example, in contactimaging systems such as the ones described in U.S. patent applicationSer. No. 14/173,500, filed Feb. 5, 2014, and incorporated here byreference.

SUMMARY

In general, in an aspect, an integral image sensor includes a sensorsurface having a surface area at which light-sensitive pixels arearranged in rows and columns. The surface area includes two or morelight-sensitive subareas each of the subareas having been configured tohave been diced from a wafer along two orthogonal dimensions to form adiscrete image sensor. The two or more light-sensitive subareas arearranged along one of the two orthogonal dimensions. The sensor surfaceof the integral image sensor is flat and continuous across the two ormore subareas.

Implementations may include one or a combination of two or more of thefollowing features. The two orthogonal dimensions along which the waferwould have been diced are parallel to the directions of the rows andcolumns of the pixels. A single row or column of the subareas isarranged along one of the two orthogonal dimensions. There areinterconnects along sides of the image sensor for making electricalcontact to the light-sensitive subareas. There are interconnects along aside or sides of a row or column that span two or more of the subareasfor making electrical contact to the light-sensitive subareas. There areinterconnects along not more than the two opposite sides of a row orcolumn that spans two or more of the subareas for making electricalcontact to the light-sensitive subareas. The surface area includes atleast one non-light-sensitive subarea between two of the light-sensitivesubareas. The non-light-sensitive subarea was configured to have becomea saw street had the wafer been diced. A sensor drive circuit is coupledto the integral image sensor. A memory is coupled to the sensor drivecircuit. A processor and an application are coupled to the memory. Achamber is associated with the sensor surface. The chamber comprises asurface spaced from the sensor surface by a predetermined distanceassociated with a monolayer of a specimen.

In general, in an aspect, an integral image sensor includes a sensorsurface having a surface area in which light-sensitive pixels arearranged in rows and columns. The surface area includes two or morelight-sensitive subareas in a row or column. Successive light-sensitivesubareas along the row or column are separated by non-light sensitiveareas. The sensor surface of the integral image sensor is flat andcontinuous across the two or more subareas.

Implementations may include one or a combination of two or more of thefollowing features. There are interconnects along sides of the imagesensor. There are interconnects along a side or sides of a row or columnthat span two or more subareas, for making electrical contact to thelight-sensitive subareas. There are interconnects along not more thanthe two opposite sides of a row or column that spans two or more of thesubareas for making electrical contact to the light-sensitive subareas.The non-light-sensitive subarea between the light-sensitive subareas wasconfigured to have become a saw street had the wafer been diced. Asensor drive circuit is coupled to the integral image sensor. A memoryis coupled to the sensor drive circuit. A processor and an applicationare coupled to the memory. A chamber is associated with the sensorsurface. The chamber includes a surface spaced from the sensor surfaceby a predetermined distance associated with a monolayer of a specimen.

In general, in an aspect, a large-area high-aspect-ratio integral imagesensor includes two or more light-sensitive subareas in a row at asensor surface. There are successive light-sensitive subareas along therow and they are separated by non-light sensitive areas. There is achamber configured to confine a monolayer of blood or other sample atthe sensor surface.

Implementations may include one or a combination of two or more of thefollowing features. The sensor surface of the integral image sensor isflat and continuous across the two or more light-sensitive subareas.There are interconnects along sides of the image sensor for makingelectrical contact to the light-sensitive subareas. There areinterconnects along a side or sides of a row or column that span two ormore of the subareas for making electrical contact to thelight-sensitive subareas. There are interconnects along not more thanthe two opposite sides of a row or column that spans two or more of thesubareas for making electrical contact to the light-sensitive areas.

A sensor drive circuit is coupled to the integral image sensor. A memoryis coupled to the sensor drive circuit. A processor and an applicationare coupled to the memory. An application is configured to perform ablood count or other analysis of the specimen. A chamber is associatedwith the sensor surface. The chamber comprises a surface spaced from thesensor surface by a predetermined distance associated with a monolayerof a specimen.

In general, in an aspect, a wafer bearing rows of image sensors issliced to separate the rows from one another. Each of the rows is slicedto form one or more large-area high-aspect-ratio sensors each comprisingtwo or more of the image sensors in a single row. The large-area sensorsare not sliced into single image sensors.

In general, in an aspect, image information is received from alarge-area high-aspect-ratio integral image sensor. The imageinformation is representative of a monolayer of a blood or otherspecimen. A blood count or other analysis is performed on the specimenusing the received image information.

In general, in an aspect, at least one component is configured toprovide two or more images of a sample, and a large-areahigh-aspect-ratio integral image sensor has two or more light-sensitivesubareas positioned to receive the two or more images from thecomponent.

Implementations may include one or a combination of two or more of thefollowing features. The component includes a beam-splitting componentconfigured to split a collimated image of the sample into two or morecopies of the collimated image, and the two or more light-sensitivesubareas are positioned to receive the two or more copies of thecollimated image from the beam splitting apparatus. An optical path fromthe beam splitting component to the large-area high-aspect-ratiointegral image sensor is free of any intervening color filter array onthe image sensor. The component is configured to acquire the two or moreimages of the sample from two or more different perspectives, and thetwo or more light-sensitive subareas are positioned to receive the twoor more images of the sample.

In general, in an aspect, a component is configured to provide two ormore images of a sample, and a large-area high-aspect-ratio integralimage sensor has two or more light-sensitive subareas positioned toreceive the two or more images from the component.

Implementations may include one or a combination of two or more of thefollowing features. The component includes a beam-splitting componentand optics to project two or more identical images of the sample on totwo or more light-sensitive subareas. There is an optical path from thebeam splitting component to the large-area high-aspect-ratio integralimage sensor. The component is configured to acquire the two or moreimages of the sample from two or more layers of the sample that lie atdifferent distances from the apparatus and to focus the images on two ormore light-sensitive subareas.

These and other aspects, features, and implementations can be expressedas methods, apparatus, systems, components, program products, methods ofdoing business, means or steps for performing a function, and in otherways.

These and other aspects, features, and implementations will becomeapparent from the following descriptions, including the claims.

DESCRIPTION

FIG. 1 is a schematic top view of a portion of a wafer.

FIG. 2 is a schematic view of a blood count device.

FIG. 3 is a perspective schematic view of a beam splitting arrangement.

FIG. 4 is a schematic view of a beam splitting arrangement.

As shown in FIG. 1, during fabrication, image sensors 12 are arranged inrows 14 along one dimension 18 across a semiconductor wafer 10, and therows are arranged side-by-side along a second dimension 20 orthogonal todimension 18. In some cases, the rows are arranged so that the imagesensors in adjacent rows are staggered as shown in FIG. 1. In somecases, the rows can be arranged so that the sensors in adjacent rows arealigned in columns.

Each image sensor has an array of light-sensitive pixels 22 alsoarranged in a pattern, e.g., a pattern of rows and columns 24, 26, alongthe dimensions 18, 20 within a light-sensitive subarea 28 of the imagesensor. Non-light-sensitive subareas 30, 32 extend throughout the waferalong the dimensions 18, 20 between adjacent light-sensitive subareas28. All of the image sensors and their pixels are exposed at a singlecontinuous smooth flat surface 33 of the wafer. In typical waferprocessing, to dice the wafer into individual discrete sensors 34, avariety of processes, such as slicing, laser cutting, or etching, can beused to remove strips of material in the non-light-sensitive subareasleaving saw streets between the image sensors.

To enable each of such discrete sensors to be connected to a sensordrive circuit that can drive the sensor and receive its image signals,interconnection contacts are formed in the wafer along opposite edges36, 38 of the image sensors that lie in each of the rows 14. When thewafer is diced, the interconnection contacts typically are accessiblefrom the top surface adjacent to the light-sensitive subarea 28 alongthe two opposite sides 44, 46 of each discrete sensor.

In some cases, in which the wafer is diced to yield discrete imagesensors, the resulting sensors could be used, for example, in digitalcamera applications or in microscopy.

In applications of such image sensors in lensless (e.g., contact)microscopic imaging, for example blood counting applications and manyothers, it can be desirable to have both a high density (resolution) ofpixels in the light-sensitive subareas and a large light-sensitive area.Image sensors typically available commercially at relatively low costmay have high pixel counts (say 10-20 megapixels in a full-framecamera-type sensor). The surface areas of such image sensors aretypically constrained by factors such as the optical features of thelenses (e.g., focal length) and cameras (e.g., aspect ratios of theintended final images) in which they will be used. The image sensors areusually rectangular and have a relatively low-aspect-ratio, say 2:1 or3:2. Some full frame camera sensors for example are 24 mm×36 mm. Largerarea sensors of various shapes and aspect ratios may be available but athigh cost based on limited production, difficulty of manufacture, theneed for custom design or other considerations.

Inexpensive, readily available larger area sensors would be useful andusable in near-field imaging applications. In theory one might form alarge-area sensor for near field imaging applications by mountingcommercially available small aspect ratio sensors as tiles in a row orin rows and columns. For many such applications, however, it can beimportant for the entire large-area of the image sensor to have a smoothcontinuous flat (i.e., coplanar) surface. Achieving such a surface usingtiled single discrete sensors can be difficult and, if possible at all,expensive.

A large-area high-resolution high-aspect-ratio image sensor 60 having acontinuous smooth flat surface 62 can be made at a relatively low costfrom an existing wafer 10 on which individual low-aspect-ratio imagesensors (such as digital camera sensors) 12 have been formed and areready for dicing as explained below. The techniques that we describe areparticularly useful if all interconnects for each individuallow-aspect-ratio image sensor on the wafer are arranged along not morethan two opposite sides of the sensor, and if all individual sensors ina row have their interconnects aligned similarly on the wafer.

To form the high-aspect-ratio sensor, instead of dicing in both of theorthogonal directions 18, 20 to form single discrete image sensors,first the wafer is sliced only in the dimension 18 along which theinterconnects are oriented, to form strips of image sensors in singlerows. Each of the rows is then sliced in the orthogonal dimension 20 toform large-area high-resolution high-aspect-ratio image sensors 60 eachhaving a desired number, say two, three, four, five, six, or more(including possibly a very large number) of sensors 64 in a row.

We use the term “large-area” broadly to include, for example, areaslarger than the light-sensitive areas of typical digital camera imagesensors, for example, areas larger than 10 square millimeters, ½ squarecentimeter, 1 square centimeter, 2 square centimeters, 5 squarecentimeters or more.

We use the term “high-aspect-ratio” to refer, for example, to an aspectratio larger than 2:1, for example, 3:1, 4:1, 6:1, 8:1 or larger.

We use the term “low-aspect-ratio” to refer, for example, to an aspectratio no larger than 2:1 or in the range between 1:1 and 2:1.

We use the term “high resolution” to mean, for example, a pixel spacingsmaller than 5 microns, or 3 μm, or 1 μm, or sub-micron.

Each of the large-area image sensors 60 has interconnection contactsalong the two opposite sides 74, 76 parallel to an axis 77 passingthrough the centers of the discrete sensors along the strip, forconnection to a sensor drive circuit 78 that can drive and receivesignals from all of the pixels of all of the discrete light sensitivesubareas of the large-area image sensor. Controlling and reading signalsfrom the multiple light sensitive subareas is possible using availabledigital camera controllers that can perform similar functions formultiple digital cameras simultaneously. Together those pixels (whichcan have a high resolution spacing) represent and can be processed togenerate a large-area image 80 which can in turn be viewed, processed,or analyzed, for example, in a blood count application.

The surface of such a large-area image sensor is as continuous, smooth,and flat as the wafer from which it is cut. The large-areahigh-resolution high-aspect-ratio image sensor 60 has a large surfacearea 82 that includes light-sensitive sub-areas 84, 85, 87 associatedwith the respective image sensors 86 in the row separated bynon-light-sensitive areas 88.

The large-area high-resolution high-aspect-ratio image sensor 60 alsohas a high-aspect-ratio (of its width to its length) that may be manytimes the aspect ratio of the single discrete image sensors that mightbe diced from the original wafer. In theory it would be possible to dicelarge-area normal aspect ratio sensors from a wafer in which each of thediced sensors would have, say, three image sensors in a row in onedimension and three columns of the image sensors in the other direction.However, such image sensors would not be practically useful because theinterconnection contacts for the edges of the sensors that were embeddedwithin the rows and columns of the sensor would be difficult orimpossible to access.

A large-area high-resolution high-aspect-ratio image sensor 60 having ahigh-aspect-ratio and some non-light-sensitive subareas might not beuseful for ordinary digital cameras or some other imaging applicationsdesigned to generate images formed by a camera lens. But for someapplications, e.g., lensless microscopic imaging for blood counting andmany others, an image sensor having a high-aspect-ratio could be usefuleven with non-light-sensitive subareas, if it thereby achieves a largeimage area, in turn providing a larger field of view. In some bloodcounting applications, the goal is accurately to identify and countvarious types of constituents in a precise tiny volume of blood that isrepresentative of blood of a person from whom a specimen was drawn. Alarger field of view results in a larger sample size, and consequentlyin more accurate counts, and can be useful in a wide variety of otherapplications. The aspect ratio of the sensor or the existence ofnon-light-sensitive subareas is not an impediment to this counting aslong as (a) the volume of blood that is imaged by the light-sensitivesubareas is known and (b) the distribution of constituents in the volumeof blood that is imaged by the light-sensitive subareas isrepresentative of the overall distribution of constituents in thespecimen. For most constituents a correct result can be achieved byassuring that the constituents have not been uncharacteristicallyconcentrated in certain places within the sample, such as at thelocations of the non-light-sensitive subareas. Approaches for assuringthe uniform distribution of constituents are described in, for example,U.S. patent application Ser. No. 15/482,215, filed on Apr. 7, 2017, andSer. No. 14/314,743, filed on Jun. 25, 2014, both incorporated here byreference.

The following four paragraphs are incorporated from U.S. patentapplication Ser. No. 14/314,743 and to the corresponding U.S. Pat. No.9,518,920, issued on Dec. 13, 2016. The references to figures and tonumerals relate to the figures of that patent.

The chamber top can be lowered relative to the sensor surface 103 toremove the excessive volume of sample from the sensor 102 and allow thesample units 97 (such as cells that are disbursed in a fluid) to beevenly distributed over the surface 103 of the sensor 102. In someimplementations, the removal of the excessive volume does not alter thebulk concentration of the sample units so that the imaging of arelatively small volume of the sample, e.g., about 40 μL, produces dataapplicable to the bulk sample, e.g., about 100 μL or more, dispensedonto the sensor. In other implementations, the new concentration isconsistently proportional to the bulk concentration of the sample units,allowing for a correction factor to be determined. To achieve thedesired sample concentration for imaging, the sample can be furtherprocessed as described further below.

The chamber top can be lowered in various ways. In one example,referring again to FIG. 2, the chamber top has a flat top surface 400and during the lowering of the chamber top, the top surface 400 is keptsubstantially parallel to the top surface 103 of the sensor 102. Wesometimes call this process a flat, linear descent.

Referring to FIGS. 3 and 4, in another example, the chamber top 95 ispositioned initially at a tilt such that one edge is against the sensor.The chamber top is then lowered at a controlled velocity profile untilflush with the sensor. We sometimes call this process a pivotingdescent. Sometimes data, such as positional variables or parameters,that control the pivoting descent can be chosen and stored, e.g., in acontroller. The pivoting descent can be performed repeatability fordifferent imaging processes (of the same sample or different samples)based on the stored data.

The descent of the chamber top can controlled by various mechanisms,e.g., manually by a human or by a machine such as an actuator 1010. Insome implementations, after one end of the chamber top is lowered andthe chamber top becomes in contact with the sample, the other end of thechamber can be raised and lowered repeatedly, e.g., without coming allthe way down to its final position. This operation may cause the sampleto rush in and out of the space between the sensor 102 and the chambertop 95, which may provide a mixing effect to the sample so that thesample units 97 are well distributed, e.g., evenly distributed, in thesample before being imaged.

Having a larger field of view is useful not just for counting, but formany microscopic imaging applications. A pathologist, for example, wouldtypically be glad to see more area of a tissue sample. The gaps due tothe non-light-sensitive areas would be minor distractions in such anapplication.

As shown in FIG. 2 (in which the elements are not shown to scale), alarge-area high-resolution high-aspect-ratio image sensor 60 can becoupled to (e.g., interconnected electrically with) a sensor drivecircuit 78 that is arranged to drive the image sensor and receive imagesignals from the image sensor corresponding to an image of a specimen 94held within a chamber 96. The chamber has a surface 97 that faces thelight-sensitive surface 98 of the image sensor and is spaced apart fromsurface 98 by a precise distance 100 that is near enough to the imagesensor to confine the specimen to a monolayer, with at least part of thespecimen within the near field distance 102 of the image sensor. Thesensor drive circuit stores the image signals from the image sensor asimage data in a data storage device 104 which may be coupled to or partof the sensor drive circuit. An application 106 executed by a processor108 coupled to the data storage device can then fetch the image datafrom the storage and apply image processing and analysis routines toperform a wide variety of tasks, such as blood counting, and provide theresults to users or other processes. The large-area high-resolutionhigh-aspect-ratio image sensor 60, sensor drive circuit 78, data storagedevice 104, processor 108, and application 106 together can comprise ablood count device 110. Additional information about lensless contactoptical microscopes, their configurations, their associated devices, andtheir uses can be found, for example, in U.S. Pat. No. 9,041,790, issuedMay 6, 2015; U.S. Pat. No. 9,518,920, issued Dec. 13, 2016; and U.S.Pat. No. 9,075,225, issued Jul. 7, 2015; and in U.S. patent applicationSer. No. 14/173,500, filed Feb. 5, 2014; Ser. No. 15/066,065, filed Mar.10, 2016; all incorporated here by reference in their entirety.

Other implementations are also within the scope of the following claims.

For example, as shown in FIG. 3, high-aspect-ratio image sensors can beused in a variety of applications other than as sensors in contactoptical microscopy. In some applications, such a sensor 120 could beused in lens-based microscopy or photography to receive and processdifferent versions of an image using light 121 from a light source 122that has passed through collimating optics 124 and a sample 126. Insteadof delivering the image directly to a single low-aspect-ratio sensor fordetection in a typical lens-based system, beam splitting devices 128(such as a beam-splitting prism) could be used to split the image intotwo (or more) similar copies 130, 132, 134 of the image, each directedalong equivalent light paths to a corresponding one of thelight-sensitive subareas 280, 282, 284 of the high-aspect-ratio imagesensors.

In some implementations, each of the images delivered from the beamsplitting device(s) can be filtered based on wavelength (for example byusing dichroic mirrors for beam splitting), permitting each of thelight-sensitive subareas to be operated in a monochrome mode, withoutthe presence of any intervening Bayer or other color filter array, toachieve highest-resolution images with multi-spectral information. Insome applications, each of the images delivered from the beam splittingdevice can be filtered based on polarization (for example by using apolarizing beam splitter). Simultaneous multi-parametric imaging of thekind that this approach would facilitate has important applications inphysiology, materials science, and other fields.

Because the light-sensitive areas all lie on a common flat surface ofthe sensor (the co-planarity is as good as it can be) and are separatedby very precisely known distances (the relative X-Y locations of thelight-sensitive areas are known precisely), in all these cases thedifferent paths from lens or lenses to the two or more light-sensitivesubareas can be arranged to have precisely the same length, and theimages delivered to the different subareas can be arranged to be ofexactly the same dimensions and focus.

As shown in FIG. 4, in some applications the paths 302, 304, 306 througha lens 307 and one or more beam splitter(s) 308, 310, 312 to thelight-sensitive areas can be arranged to have precisely different(rather than identical) lengths, such that the images formed on the twoor more light-sensitive areas 314, 316, 318 will be aligned on thecommon plane of the light-sensitive areas but have different objectplanes 330, 332, 334 in focus, permitting simple simultaneoushigh-resolution multifocal imaging, amenable to further interpolation bycomputational means. In some cases, such as the one shown in FIG. 4, theappropriate different path lengths are achieved by tilting the stripbearing the light-sensitive areas at an angle to the optical axis 350.Other ways of achieving the appropriate different path lengths are alsopossible.

These conditions and scenarios described above can all be achieved bycareful placement and orientation of the beam-directing optics, butwithout requiring efforts that would otherwise be required to align thesurfaces of discrete sensors on a common plane and at a precise knownseparation between the subareas.

1.-40. (canceled)
 41. A method comprising situating a sample on a samplesurface of a large-area high-aspect-ratio integral image sensor, thesensor comprising two arrays of photosensitive elements arranged toreceive light passing through the sample and onto the sample surface,the two arrays being separated by a non-photosensitive interveningregion of the sensor, the sample including portions situated on the twoarrays and a portion situated on the non-photosensitive interveningregion of the sample surface, storing data about light received at thetwo arrays after passing through the sample, without regard to lightreceived at the non-photosensitive intervening region, processing thestored data to derive information about one or more constituents of thesample, and treating the derived information as representative of theone or more constituents of the portions of the sample situated on thetwo arrays and the portion of the sample situated on thenon-photosensitive intervening region of the sample surface.
 42. Themethod of claim 41 in which the two arrays of photosensitive elementsoccupy rectangular regions of the sensor and the non-photosensitiveintervening region is rectangular.
 43. The method of claim 41 in whichprocessing the stored data comprises: counting units of a firstconstituent of the sample in the portions situated on the two arrays,and determining a count of the first constituent per unit volume of thesample including the portion situated on the non-photosensitiveintervening region of the sample surface, based on the counted units ofthe first constituent and a known volume of the portions of the samplesituated on the two arrays.
 44. The method of claim 41 in which the oneor more constituents of the sample comprise a countable constituent ofblood.
 45. The method of claim 41 in which situating the sample on thesample surface comprises applying the sample to achieve similardistributions of the one or more constituents of the sample in theportions situated on the two arrays and the portion situated on thenon-photosensitive intervening region.
 46. An apparatus comprising alarge-area high-aspect-ratio integral image sensor comprising a samplesurface configured to receive a sample, the sample surface comprisingtwo arrays of photosensitive elements separated by a non-photosensitiveintervening region of the sensor, the two arrays and thenon-photosensitive intervening region being arranged to receive lightpassing through portions of the sample situated on the two arrays and aportion of the sample situated on the non-photosensitive interveningregion of the sample surface; a storage; at least one processor; andstored instructions that, when executed by the at least one processor,cause the at least one processor to perform operations comprisingstoring, in the storage, data about light received at the two arraysafter passing through the sample, without regard to light received atthe non-photosensitive intervening region, processing the stored data toderive information about one or more constituents of the sample, andtreating the derived information as representative of the one or moreconstituents of the portions of the sample situated on the two arraysand the portion of the sample situated on the non-photosensitiveintervening region of the sample surface.
 47. The apparatus of claim 46in which the two arrays of photosensitive elements occupy rectangularregions of the sensor and the non-photosensitive intervening region isrectangular.
 48. The apparatus of claim 46 in which the operationscomprise counting units of a first constituent of the sample in theportions situated on the two arrays, and determining a count of thefirst constituent per unit volume of the sample including the portionsituated on the non-photosensitive intervening region of the samplesurface, based on the counted units and a known volume of the portionsof the sample situated on the two arrays.
 49. The apparatus of claim 48in which determining the count of the first constituent per unit volumeof the sample is performed based on assuming that a concentration of thefirst constituent in the portions situated on the two arrays matches aconcentration of the first constituent in the portion situated on thenon-photosensitive intervening region.
 50. The apparatus of claim 46 inwhich the one or more constituents of the sample comprise a countableconstituent of blood.